For the amount of money you would spend on a B-kit you would probably be better off doing a 4" intake, wedge, prop, exhaust, SC impeller, XS power intercooler. Just my 2 cents. I'm about to start the same project here shortly.

Riva claims around 70 with their stage II kit. I'm a fan of kits. They contain all the parts need to install-little things like bolts and clamps. Or look at the stage II kit and pick a choose parts that are in the kit and replace them with more ideal ones. For example, instead of the vortech supercharger impeller go with the rotax one. Just some food for thought